The progressive degradation of the wastes disposed of in landfill sites generates landfill gas which is largely a combination of methane (approximately 60%) and carbon dioxide (approximately 40%). There are also trace components such as hydrogen sulphide which can cause landfill gas to become odorous. In a hazardous landfill the quantity of landfill gas is much less than a typical domestic landfill but ENRMF still has full gas control systems to ensure that any gas generated is appropriately managed.

At ENRMF air quality is monitored in the surrounding boreholes and in the ambient air on a monthly basis.

Below are presented graphs showing the available results for the last 12 months of monitoring of methane in boreholes and the ambient air and hydrogen sulphide in the ambient air.

Methane in boreholes

Methane is monitored in boreholes to confirm that landfill gas generated in the landfill is not migrating from the site into the surrounding ground.  Methane is not toxic but it is a greenhouse gas and is flammable so it must be controlled.  Methane can however be generated by the breakdown of vegetation hence detection of the gas must be interpreted in the context of the surrounding environment.  A trigger level of 1% methane has been set by the Environment Agency which is well below a concentration of concern.

The results show that little or no methane has been detected in the boreholes around the site over the past 12 months.

Ambient methane

The purpose of monitoring ambient methane is principally to confirm that significant amounts of this greenhouse gas are not escaping from the site.  Ambient methane is measured by walking around the site boundary with a hand held meter.  The concentration is measured in parts per million (1ppm = 0.0001%). 

The graphs show that the maximum detected concentration of methane detected at the boundary in the last 12 months is less than half the trigger level. 

Ambient hydrogen sulphide

Hydrogen sulphide is the cause of the smell known as rotten eggs.  At high concentrations it can be poisonous.  It is monitored largely because of its odour generating potential. Ambient hydrogen sulphide is measured by walking around the site boundary with a hand held meter.  The concentration is measured in parts per million (1ppm = 0.0001%).  Hydrogen sulphide is only measured if methane levels are elevated.  No elevated levels of methane have been monitored so it has not been necessary to monitor hydrogen sulphide.